hosts檔案的位置在C:\WINDOWS\system32\drivers\etc\hosts
有些惡意網站或軟體會篡改這個檔案
但有些防毒之類軟體也會經由修改這個檔案來達到保護使用者避免連上惡意網站
像Spybot - Search & Destroy就會把惡意網站對應到127.0.0.1
網站若被對應到127.0.0.1會連不上

以上2種情形都有可能禁止其他程序更動此檔案
不知樓主是哪種情形
你可用記事本開這個檔案自己看看那些被對應到127.0.0.1的網站大概都是些什麼
不過我記得這個方法似乎只對IE核心的瀏覽器或調用IE的軟體有效
其他不同核心的瀏覽器不會去讀這個檔案自然是一點用也沒有

感謝你的回答
我用記事本開啟host , 結果如下:
# Copyright (c) 1993-1999 Microsoft Corp.
#
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
#
# This file contains the mappings of IP addresses to host names. Each
# entry should be kept on an individual line. The IP address should
# be placed in the first column followed by the corresponding host name.
# The IP address and the host name should be separated by at least one
# space.
#
# Additionally, comments (such as these) may be inserted on individual
# lines or following the machine name denoted by a '#' symbol.
#
# For example:
#
# 102.54.94.97 rhino.acme.com # source server
# 38.25.63.10 x.acme.com # x client host

127.0.0.1 localhost
# Start of entries inserted by Spybot - Search & Destroy
127.0.0.1 www.007guard.com
127.0.0.1 007guard.com
127.0.0.1 008i.com
127.0.0.1 www.008k.com
127.0.0.1 008k.com
127.0.0.1 www.00hq.com
127.0.0.1 00hq.com
127.0.0.1 010402.com
127.0.0.1 www.032439.com
127.0.0.1 032439.com
127.0.0.1 www.0scan.com
127.0.0.1 0scan.com
127.0.0.1 www.100888290cs.com
127.0.0.1 100888290cs.com
127.0.0.1 www.100sexlinks.com
127.0.0.1 100sexlinks.com
127.0.0.1 www.10sek.com
127.0.0.1 10sek.com
127.0.0.1 www.123topsearch.com
127.0.0.1 123topsearch.com
127.0.0.1 www.132.com

我實在搞不清楚這個情形是... , 我最近都是用Firefox上網
幾乎不用IE7

這個應該是保護機制吧?
避免使用者電腦開啟這些網站

像大砲開講就有提供避免連結至惡意網站的hosts
將這些惡意網站的IP設為127.0.0.1(本機),就等於開啟這些網站是連自己電腦,相當於[無效化]
http://rogerspeaking.com/2008/04/720